Serial Interface COM2 of the Terminal Bases

Note

The serial interface COM2 is not available at:

• Processor Modules with type designator -2ETH (e. g. PM591-2ETH)
• Processor Modules PM56xx

The serial interface COM2 is connected via a 9-pole SUB-D connector. It is not intended to use COM2 to establish a CS31 system bus. It is configurable for RS-232 or RS-485 and can be used for

• online access
• a free protocol
• MODBUS RTU, master and slave

If the RS-485 bus is used, each interconnected bus line (each bus segment) must be electrically terminated. The following is necessary:

• 2 resistors of 120 Ohms each at both line ends (to avoid signal reflections)
• a pull-up resistor at RxD/TxD-P and a pull-down resistor at RxD/TxD-N. These 2 resistors care for a defined high level on the bus, while there is no data exchange.

It is useful, to activate both the pull-up and the pull-down resistors, which only are necessary once on every bus line, at the bus master.

Pin assignment

Serial Interface	Pin	Signal	Interface	Description
	1	FE	-	Functional earth
	2	TxD	RS-232	Transmit data	Output
	3	RxD/TxD-P	RS-485	Receive/Transmit	Positive
	4	RTS	RS-232	Request to send	Output
	5	SGND	Signal ground	0 V supply out
	6	+5 V	-	5 V supply out
	7	RxD	RS-232	Receive data	Input
	8	RxD/TxD-N	RS-485	Receive/Transmit	Negative
	9	CTS	RS-232	Clear to send	Input
	Shield	FE	-	Functional earth

Attention

:strong:Risk of corrosion!

Unused connectors and slots may corrode if XC devices are used in salt-mist environments.

Protect unused connectors and slots with TA535 protective caps for XC devices TA535: Protective Caps TA535 for XC Devices TA535 - Protective Caps for XC Devices.

The following drawing shows an RS-485 bus with the bus master at the line end.

If the master is located within the bus line, it does not need a terminating resistor. The pull-up and the pull-down resistors, however, are necessary:

Attention

If the bus is operated with several masters, the pull-up and pull-down resistors may only be installed at one master.

The cable shields must be earthed. See CS31 System Bus CS31 bus.